Airtight lid for container and method of use

ABSTRACT

A lid for forming an airtight seal to a bowl or dish plate to elongate the life of product therein comprises an impermeable membrane having an outer perimeter larger than the rim of the container and an enforcement ring for enabling the formation of an airtight seal between the membrane and rim of the container under vacuum. The membrane is sufficiently soft to cause it to fill the lower sections or imperfections on the rim, thus enabling the lid to form an airtight seal to almost all household containers. The membrane may be adapted to have sufficient low tensile stress, thereby preventing the vacuum in the container from imploding or collapsing the container even if it has a thin or weak wall. The enforcement ring has vertical and horizontal rings connected to the membrane perimeter to prevent the membrane deformation at both vertical and horizontal directions. The lid may further comprise an air evacuation passageway having an air collection chamber for extracting air from the container and a valve for allowing air to flow out of the container but preventing air from entering. In use, the lid may be sealed to a container by simply pushing the membrane into the container and releasing the membrane to generate a vacuum to affix the membrane to the container, or may be sealed to a container by connecting a vacuum generator to the evacuation passageway to evacuate the container.

FIELD OF THE INVENTION

This invention relates to a lid for containers, and particularly to a lid that forms an airtight seal to the Container to protect the contents such as food against deterioration or prevent the leakage of the contents therein.

BACKGROUND OF THE INVENTION

To slow down the deterioration, food and other spoilable products have been traditionally sealed in a plastic bag by a vacuum packaging system such as a FoodSaver® from Tilia Inc. or in a special container with a specially designed lid having a seal gasket. Normally, users have to transfer the products from their original containers to the plastic bags or special containers, which causes significant inconvenience to the users.

Besides the inconvenience, the traditional method of protecting spoilable products presents several other challenges to the users or consumers. The first one is that this method limits consumers' choices to the plastic bags and special containers, disallowing users to use their favorite containers such as bowls or dish plates, which are readily available in kitchens, to store food and other spoilable products. Unlike the special containers, conventional bowls and dish plates do not have the flat and even rim required to form a watertight or airtight seal with the lid. In addition, the conventional bowls and plates may not have the strength to withstand the vacuum and may implode as a vacuum is drawn therein.

The second challenge is the high cost of the special containers and the lids. Because the special containers must have a very flat and even top surface for the rim in order to form an airtight seal with the lid, unlike the conventional ceramic or porcelain bowls and plates made from inexpensive earth or glass they must be made from more expensive materials such as plastics or metals by more expensive process such as injection molding and metal forming.

The third challenge is the time required to seal the food or other spoilable products. For example, to seal a leftover meal, one need to transfer the meal from an original container such as a dish plate or bowl to the special container or plastic bag, to evacuate the special container or plastic bag with a vacuum packaging appliance, and clean the original container. This process seems not very complex, but it is too time consuming to many people who are squeezed in time for work and other life events.

The present invention is to provide a new container lid to simplify the process of sealing food and other spoilable products and to resolve the challenges above.

SUMMARY OF THE INVENTION

The invention provides a lid for forming an airtight seal to a container such as a bowl or dish plate to elongate the life of product therein. The lid comprises an air impermeable membrane having an outer perimeter larger than the rim of the container and an enforcement ring for enabling the formation of the airtight seal between the membrane and rim of the container under vacuum or subatmospheric pressure. The impermeable membrane is sufficiently flexible and soft to enable the part of the membrane that is directly above the rim of the container to conform to the topography of the rim so that the membrane enters or fills any lower sections or other imperfections, which are common for most household containers, on the rim of the container. As a result, the membrane can prevent any air gap from forming between the membrane and the rim, and enable the lid to form an airtight seal with most household containers. The enforcement ring is made from a metal material such as steel and aluminum and has two horizontal rings connected by a vertical ring for clamping the membrane at its outer perimeter to prevent the deformation of the membrane at both vertical and horizontal directions.

The lid may further comprises an air evacuation passageway having an air collection chamber for extracting air from the container and a valve for allowing air to flow out of the container but preventing air from entering the container. The collection chamber has collection channels for delivering air to the valve, a microporous film and a side wall to which the film and membrane are attached. The valve comprises a valve opening, a seal member for closing the valve opening, and a slender member adapted to allow one to open the valve to release the vacuum in the container and to prevent unintended release of the vacuum when the slender member is accidentally touched by another container or object.

To use the lid according to one embodiment of the invention, one simply places a product into the container, places the lid on, pushes the membrane into the container to cause air to escape from the evacuation passageway, and then releases the membrane. This produces a vacuum or subatmospheric pressure in the container to affix the membrane to the container and to improve the life of the product. It is important that in order to generate and maintain the vacuum in the container, the impermeable membrane should have a sufficient low tensile strength and have a tendency to return to its original shape.

To use the lid according to another embodiment of the invention, one places a product into the container, places the lid on, connects a vacuum generator to the evacuation passageway, and evacuates the air in the container. The membrane is adapted to have sufficient low tensile stress to enable the vacuum to cause the membrane to enter the container and to conform to the topographies of the side wall of the container and the product. In contrary to the traditional belief that a vacuum container must have a strong and thick wall and in contrary to what is taught by home vacuum packaging industry leaders including FoodSaver®, it was discovered that the lid of the present invention can enable most containers found in a household kitchen to withstand a vacuum generated by home vacuum packaging appliances such as the FoodSaver® vacuum sealers. By making the air impermeable membrane sufficiently expandable or stretchable, by making the membrane tensile stress sufficiently low and by making the membrane sufficiently thin, the lid was discovered to even enable a vacuum to be produced in a disposable foam tray without imploding or collapsing foam tray.

It is an object of the present invention to provide a lid capable of consistently forming an airtight seal to almost all household containers even if they have imperfect rims;

It is a further object of the present invention to provide a vacuum lid capable of consistently forming an airtight seal to almost all containers under vacuum even if the containers have thin or weak walls;

It is a further object of the present invention to provide a vacuum package that will not crush or damage delicate or crushable products;

It is a further object of the present invention to provide a lid capable of consistently forming an airtight seal to a container and of introducing hot gaseous fluid into the container;

It is a further object of the present invention to provide a vacuum lid capable of readily forming an airtight seal to a container and of readily releasing the vacuum therein;

It is a further object of the present invention to provide a vacuum lid that can elongate the length of time the vacuum can be maintained in the container.

These and other objectives and advantages of the present invention will become apparent from the following description of the preferred embodiments, taken together with the accompanying drawings.

DESCRIPTION OF THE DRAWING

The accompanying drawing illustrates diagrammatically non-limitative embodiment of the invention, as follows:

FIG. 1 is a section view of a lid and a dish plate before a seal is formed;

FIG. 1 a is a section view of the lid along line A-A of FIG. 1;

FIG. 2 is a section view of the lid and dish plate of FIG. 1 after being vacuum-sealed;

FIG. 2 a is a section view of the lid and dish plate of FIG. 1 after a vacuum seal is formed by simply pushing the lid;

FIG. 3 is a sectional view of a lid according to a second embodiment of the invention;

FIG. 3 a is a section view of the lid of FIG. 3 after forming a vacuum seal to a bowl by manually pushing the lid;

FIGS. 3 b and 3 c are sectional views of two modified versions of the lid of FIG. 3;

FIG. 4 is a sectional view of a stack of lids according to a third embodiment of the invention;

FIG. 4 a is a section view of the lid along line A-A of FIG. 4;

FIG. 4 b is a section view of the lid of FIG. 4 after forming a vacuum seal to a bowl by manually pushing the lid to produce a vacuum in the bowl;

FIG. 4 c is a section view of the lid of FIG. 4 after forming a seal to a dish plate by manually stretching the elastic side wall of the lid to fit into the rim.

FIG. 5 is a section view of a lid, a dish plate and a vacuum device before a seal is formed according to another embodiment of the invention;

FIG. 5 a is a section view of the lid and dish plate of FIG. 5 after the vacuum seal;

FIG. 5 b is a section view of the lid and a flatter dish plate after the vacuum seal;

FIG. 6 a section view of a lid, a dish plate and a vacuum device before a seal is formed according to another embodiment of the invention;

FIG. 6 a is a section view of the lid and dish plate of FIG. 6 after the vacuum seal;

FIGS. 7 a and 7 b are section views of two exemplar membranes used for the lid of the invention;

FIG. 8 is a section view of a lid according to another embodiment of the invention;

FIG. 8 a is a section view of a lid of FIG. 8 after being sealed to a dish plate 8 a;

FIG. 9 is a section view of a lid and a lid support according to another embodiment of the invention;

FIG. 9 a is a section view of a lid, lid support of FIG. 10 that are vacuum sealed to a dish plate;

FIG. 10 is a section view of a lid for introducing hot gaseous fluid from a generator into a container according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 1 a illustrate a lid 1 for a bowl or plate 20 having an open top end 23, a rim 21, a bottom 25, a side wall 22 and a chamber 27 to receive several fruits 26. Like most containers in a household, the rim 21 for bowl 20 is not perfectly flat, and may be warped or have one or more lower sections 28. Such warping or lower sections 28 would cause a gap between the currently known or available lid and the rim 21, preventing the current known lids from forming an airtight seal to the container. The lid 1 of the present invention comprises an air impermeable membrane 3 having an outer perimeter 2 larger than the rim of the container to cover the container and an enforcement ring 8 for preventing the outer perimeter of the membrane from deformation when the membrane is pulled into the container by either a subatmospheric pressure or vacuum (FIG. 2) or is pushed into the container by hand or force (FIG. 2 a).

The enforcement ring 8 is made from a metal material such as steel and aluminum, and has two horizontal rings 91 connected by a vertical ring 92 for clamping the membrane at its outer perimeter. The horizontal ring 91 contributes largely to preventing the deformation of the membrane at horizontal direction and the vertical ring 92 contributes largely to preventing the deformation of the membrane at the vertical direction. The enforcement ring, which is shown to have a round or oval shape in FIG. 1 a, may also have a rectangle, square, triangle, hexagon or other shape. It was found that a round shape, an oval shape, or a square or rectangle shape with its four corners rounded helps preventing the enforcement ring from deformation at the horizontal direction. It was also found that without enforcement ring 8, the membrane 8 would not form an airtight seal to rim 21 of the container, thereby not allowing a subatmospheric pressure or vacuum to form in the container.

The air impermeable membrane 3 is designed to enable the part of the membrane that is directly above the rim 21 of the container to conform to the topography or shape of the rim so that the membrane enters or fills the lower section 28 (FIGS. 2 and 2 a), thereby preventing any air gap from forming between the membrane and the rim 21 of the container. As a result, the lid 1 of the present invention can form an airtight seal and vacuum with most containers such as bowls, dish plates, pans, cups, canisters, trays, bottles and jars found in one's home. To prevent air from diffusing into and the flavor, moisture or smell product in the container from diffusing out of the container, the membrane comprises a barrier material or layer that can retain its barrier to air, flavor and moisture even after the membrane is significantly expanded or stretched into the container, which barrier along with the membrane structure will be discussed in FIGS. 7 a and 7 b.

An air evacuation passageway 63 for the lid comprises an air collection chamber 18 for extracting air from the container and a valve 94 for allowing air to flow out of the container but preventing air from entering the container. The collection chamber 18 comprises a left and right collection channels 4 a and 4 b for collecting and delivering air to the valve 94, a round center wall 40, a film 9 having numerous microscopic pores, and a side wall 10 having a bottom surface 7 whose inner peripheral area 7 a sealed to the film 9 and outer peripheral area 7 b sealed to the membrane 3. The valve 94 comprises a cylindrical body 15, a valve base 17 having an valve opening 5, a seal member 6 above the base for closing the valve opening, and a retainer 16 having a plurality of protrusions to retain the seal member within body 15. The valve also has an elongated member 12 with its one end connected to the seal member and the other end 11 extended out of the cylindrical opening of the body 15 to allow one to pull the seal member away from the valve opening to release the vacuum in the container. The elongated member 12 is preferably to be a thin flexible member such as a string, a strip and a wire. The flexibility of the member 12 prevents unintended release of the vacuum in the container 20 when the elongated member is accidentally touched by another container or object. The thinness of the elongated member allows the cylindrical opening of the body 15 to receive a vacuum tube from a conventional vacuum packaging device to evacuate the container. It is appreciated that valve 94 with the flexible elongated flexible member 12 can be used to release vacuum in conventional vacuum packaged cans or canisters.

The film 9 has numerous microscopic openings adapted to allow air to exit the container but to prevent particulate or solid matters from passing through, thereby preventing the loss of product when the container is evacuated via said evacuation passageway. Such film can be a microporous membrane such Supor® polyethersufone membrane from Pall Corp., a woven filter or a nonwoven filter. It was discovered that by using a hydrophobic film such as Gore-Tex® from W. L. Gore Associates or porous polypropylene or polyethylene film, the film became impermeable when liquid in the product in the container reaches the film. As a result, such a hydrophobic film will prevent the loss of liquid in the product 26 through the evacuation passageway 63 when the container is evacuated. It was also discovered that when film 9 is sufficiently hydrophobic, it can retain its permeability to air after the liquid in the product leaves the film. It was also found that by coating or impregnating the porous film 9 with certain gel forming materials such as starch, the film allowed air to pass through readily, but became non-porous and impermeable to both air and liquid when the liquid in the product reaches the film to cause gel to form in the film. Like a hydrophobic film 9, such a gel-forming film will prevent the loss of liquid in the product 26 when the container is evacuated.

According to a first exemplar application for the lid 1 of the invention, one simply places a product 26 such as fruits, meat or meals into the container 20, places the lid on the container in a way that the enforcement ring 8 is outside the rim of the container, pushes the membrane 3 into the container to cause air to escape from the evacuation passageway 63 by pressing the membrane directly or the top wall of the evacuation chamber 18, and then releases the membrane. This produces a vacuum or subatmospheric pressure between the membrane and container to affix the impermeable membrane 3 to the container as shown in FIG. 2 a as well as to improve the life of the product 26. Here the evacuation chamber also functions as a push facilitator to facilitate the pressing and removal of air. It is important that in order to generate and maintain the subatmospheric pressure or vacuum in the container, the impermeable membrane 3 has a sufficient low tensile stress or strength and have a tendency to return to its original shape. The membrane may be a very thin stretchable plastic membrane such as an 0.0006″ thick linear or ultra linear low density polyethylene membrane or an 0.001″ thick multilayer membrane containing an EVOH barrier layer and low density polyethylene skin layer, or may be a thermoplastic elastomer or rubber membrane such as a butyl rubber, ethylene acrylic elastomer or ethylene propylene (i.e. EPDM) elastomer membrane. It was discovered that the lid 1 comprising a thin elastomer or rubber membrane 3 could maintain the subatmospheric pressure to affix the membrane to the container 20 for significantly longer period of time than the lid 1 comprising a thin stretchable plastic membrane.

According to a second exemplar application for the lid 1 of the invention, one places a product 26 into the container 20, places the lid on the container in a way that the enforcement ring 8 is outside the rim of the container, places a vacuum generator 41 onto the round center wall 40 of the evacuation chamber 63 to evacuate the container, and then removes the vacuum generator. The membrane 3 is adapted to have sufficient low tensile stress to enable the vacuum to cause the membrane to elongate to enter the container 20 and to conform to the topographies of the side wall 22 of the container 20 and the product 26 as shown in FIG. 2 b. The top part of the product 20 is wrapped around by the impermeable membrane 3 to show the shape of the product. The membrane is preferably transparent to light to make the product in the container visible. It is appreciated that an effective amount of an antifogging additive such as glyerine mono-oleate added to the membrane 3 would significantly improve the visibility of the product through the membrane, especially when the product has high moisture content.

The vacuum generator 41 comprises a vacuum pump 46, a battery 50 for the pump, a skirt 44 having a seal ring 42 to seal to the round wall 40 of the lid, and an electric switch 51 for the pump. The pump 46 comprises a motor 48 with a shaft 47 affixed to a disc 49, a pin 54 on the disc to translate the disc rotation movement to a repetitive linear movement of a piston 56 connected to the pin by a beam 55 and a hole 52 at the end of the beam to receive the pin, and a piston chamber having check valves 45 and 64 arranged to produce a vacuum inside the skirt 44 as the motor after the motor 48 is turned on. It is appreciated that the container 20 may also be evacuated by inserting a vacuum tube from any vacuum device such as a FoodSave® vacuum sealer into the top opening of the body 15.

In contrary to the traditional belief that a vacuum container must have a strong and thick wall and in contrary to what is taught by home vacuum packaging industry leaders including Tilia Direct Inc which sells FoodSaver® Universal vacuum lids and vacuum canisters, it was found that the lid 1 of the present invention can enable most containers found in a household kitchen to withstand a vacuum generated by home vacuum packaging appliances such as the FoodSaver® vacuum sealers. It was even found that by making the air impermeable membrane sufficiently expandable or stretchable, by making the tensile stress of the membrane sufficiently low at significant elongation and by making the membrane sufficiently thin, the lid 1 can even enable a vacuum to be produced in a disposable foam tray without imploding collapsing foam tray. It is theorized that the intimate contact between the gas impermeable membrane and the container wall helps preventing the container from being imploded or collapsed by the vacuum. To enable a container having a thin or weak wall to withstand vacuum, the air impermeable membrane 3 has a tensile stress lower than about 5R_(m)/L, preferably lower than 2R_(m)/L, pounds per square inch or Psi at a tensile strain of approximately 20% to 50% elongation, where R_(m) is the radius or equivalent radius of the membrane 3 or the rim 21 of the container 20 and L thickness of the membrane in inches. The equivalent radius is used if the container 20 or the membrane 3 of the lid has a non-circular perimeter, and is defined by the formula of R_(m)=(A/3.14)^(1/2), where A is the area of the impermeable membrane 3 or the opening 23 of the container.

It is also known that when a fragile or delicate product such as berries, pre-cut watermelon pieces or French fries is placed in a bag such as a FoodSaver® bag and the bag is evacuated by a vacuum seal appliance, the fragile or delicate would be crushed or smashed by the bag. It was discovered that by making the impermeable membrane 3 of the lid highly expandable and making the tensile stress of the membrane lower than 2R_(p)/L, preferably lower than 0.5 R_(p)/L, pounds per square inch or Psi at a tensile strain of approximately 20% to 50% elongation, the fragile or delicate 26 in the container 20 became much less prone to be crushed or smashed by the vacuum, where R_(p) is the radius or equivalent radius of product 26 and L is membrane thickness in inches. The equivalent radius is used if the product 26 is not of a ball shape, and is defined by the formula of R_(m)=(V/4)^(1/3), where V is the volume of the product. For examples, grapes and blueberries are of a ball shape with a radius of approximately 0.3 inches, the tensile stress of the membrane is preferred to be lower than 30 Psi if the membrane thickness is 0.005″. For comparison purpose, the films in existing bags (e.g. FoodSaver® bags) for vacuum packing is about 3000 Psi, which is believed to be needed to prevent the puncture of the bag by the product.

To meet such extremely low tensile stress requirement, the membrane can be made from elastomer or rubber materials such as butyl rubber, ethylene acrylic elastomers, ethylene propylene (or EPDM) rubber, natural rubber, polyurethane elastomers, styrene-containing block copolymer elastomers, Santoprene elastomer and polychroroprene elastomer with a durometer hardness lower than about 70 shore A units, preferably less than about 55 shore A units. Butyl rubber, ethylene acrylic elastomers and polychroroprene elastomer are the preferred materials since the membrane made from them maintains a vacuum in the container for a significantly longer period time than the other rubber materials. The impermeable membrane 3 with such extremely low tensile stress may also be achieved by coating, extruding or co-extruding a very thin layer of barrier polymers such as a 0.0001″ layer of poly(ethylene vinyl alcohol) or EVOH with a relatively thicker layer of elastomer, as will be discussed in FIGS. 7 a and 7 b. It is appreciated that the air-impermeable membrane 3 with such extremely low tensile stress may also be used to make new crush-resistant bags for packing fragile fruits, salads, vegetables, French fries and other fragile and crushable or delicates under vacuum.

To enable the vacuum or subatmospheric pressure in the container to last for an extended period, the impermeable membrane should have a tensile stress sufficiently low to reduce the rate of air diffusion through the membrane into the container. It was discovered that by when the tensile stress of the membrane 3 was reduced from about 500 Psi to about 200 Psi at the same tensile strain, the vacuum in the container lasts significantly longer or the membrane stays sealed to the container for significantly longer time. To reduce the loss of vacuum in the container 20, the membrane should have a tensile stress lower than 7R_(m)/L, preferably lower than 4R_(m)/L pounds per square inch or psi at a tensile strain of 20% to 50% elongation, wherein R_(m) and L have been defined above.

It was also discovered that when by coating or including a thin layer of fluid such as a liquid, paste or gel layer at least on the lower surface of the membrane, the vacuum in the container lasted significantly longer. It was also discovered that by having a tacky or adhesive material layer on the membrane 3 to cause it to reversibly adhere to the container 20, the vacuum in the container also lasted significantly longer.

FIG. 3 shows a first modified version of the lid 1 of FIG. 1 with a plate-shaped push facilitator 38 for facilitating the pushing of the membrane into the container by hand, an improved evacuation passageway 63 to lower the cost of the lid 1 and a pre-formed cavity 14 and side wall 35 on the impermeable membrane 3 to improve the seal to the rim 21 and side wall 22 of the container. The improved evacuation passageway has an valve 94 comprising opening 6 on the membrane, a valve base 17 on the membrane around the opening, a seal disc member 6, a elongated flexible member 12 having one end connected to the seal member and another end 11 outside the valve for one to pull and open the valve to release the vacuum in the container, and a retainer 16 comprised of a horizontal wall formed on push facilitator 38. A cylindrical wall 53 is formed on the push facilitator for receiving a vacuum tube from a vacuum device such as a FoodSave® vacuum sealer if desired. To use, one places lid 1 onto container 20 and cavity 14 automatically falls into the container to facilitate the seal to side wall 22 of the container. One then push the facilitator 38 to stretch the side wall 35 of the membrane to drive air out of the passageway 63, and stops the pushing to cause a vacuum to form below the membrane to affix the membrane to the container by the vacuum (FIG. 3 a). It was found that by coating the seal member 6 with a thin fluid layer such as a high-boiling point liquid like cooking oil, a gel or a paste, the vacuum could be maintained in the container for a longer time. It is appreciated that if the top surface of the product 26 protrudes out of the container 20, the side wall 35 enables the push facilitator 35 to move upwards so that the product will not prevent the membrane from forming a seal to the rim 21 of the container.

FIG. 3 b shows a second modified version of the lid 1 of FIG. 1. The modified lid is similar to that of FIG. 3 except that it has a smaller enforcement ring 8 and membrane 3 to fit into jars, bottles and other containers with small openings 23 and has a valve 94 that stays closed after the loss of vacuum below the membrane 3. In the valve 94, the seal member 6 is connected to retainer 16 below the valve opening 5 by a stem 43 to sandwich the membrane and valve base 17 between the seal member 6 and the retainer 16. The stem 43 is short enough to cause the seal member 6 to press against the membrane around the opening 5 slightly so that the valve stays closed even after the vacuum in the container (not shown) below the membrane 3 is released. Two or more openings 24 are formed on the retainer 16 to make the retainer more flexible.

FIG. 3 c shows a third modified version of the lid 1 of FIG. 1. The modified lid is similar to that of FIG. 1 except that it has a smaller enforcement ring 8 and membrane 3 to fit into jars, bottles and other containers with small openings 23, a plate-shaped push facilitator 38 for facilitating the pushing of the membrane into the container by hand, an improved evacuation passageway 63 to lower the cost of the lid 1. The evacuation passageway comprises a valve 94 having a seal member 6 located below the membrane 3 to seal the valve opening 5 formed on the membrane, a retainer 16 above the valve opening and connected to the seal member by stem 43, and a loaded spring 33 to cause the seal member to press the membrane and close the valve opening after the loss of vacuum in the container (not shown) below the membrane. The retainer 16 also functions as a button 84 for one to push. To seal a container with the lid 1, one places the lid on the container, presses the button 8 or push facilitator 38 with sufficient force push the membrane 3 into the container, and then releases the button to cause a vacuum in the container. To remove the lid, one press the button 84 to push the seal member 6 down to release the vacuum, but the pressing is sufficiently slight that the membrane 3 can return to its original shape to move out of the container to allow the lid to be removed.

FIG. 4 shows a forth modified version of the lid 1 of FIG. 1. In this modified lid, the air impermeable membrane 3 has a side wall section 35 and a horizontal center section 127. The side wall section 35 of the membrane is elastic or rubbery and at least part of the side wall section 35 has a perimeter smaller than the rim 21 of the container. Such a configuration enables the side wall section 35 to form an airtight seal to the rim 21 of the container 20 (FIGS. 4 b and 4 c). The enforcement ring 8 is larger in diameter than the side wall section 35 of the membrane to facilitate the mounting of the lid to the container. In FIG. 4 b, the enforcement ring 8 is larger than the rim 21 of the container, allowing one to seal the container by simply pulling the enforcement ring 8 of the lid downward to stretch or expand the side wall section 35 so that the section wall section seals to the rim 21 the elastic force. To reduce the force needed to expand the side wall section 35 to seal to the rim of the container, the side wall section is made to have sufficiently low tensile stress strength.

The enforcement ring 8 may also be made elastic to allow the lid to seal to the containers having rim 21 larger than the enforcement ring (FIG. 4 c). One may press the horizontal center section 127 to push it into the container 20 to evacuate some air out of the container and then release the membrane to cause a vacuum in the container to help affix the membrane to the container (FIG. 4 c). It is appreciated that a simple evacuation passageway (not shown) may be formed on the membrane to allow air to exit the container, thereby reducing the force needed to push the membrane 3 into the container. The evacuation passageway may have a valve opening on the horizontal center section 127 and a seal member such as a flexible film over the opening to allow air to exit the container. It is also appreciated that the horizontal center section 127 of the membrane 3 may be a plastic or metal sheet attached to the lower end of the side wall section 35.

FIG. 5 shows a fifth modified version of the lid 1 of FIG. 1 for use with a vacuum generator 41 that is similar to the vacuum generator of FIG. 2 b but has a larger skirt or chamber 44 to enclose lid 1 and the container 20. The vacuum device further has a release valve 66 having an opening 61 on skirt 44, a button 58, a seal disc 62 connected to the button by a stem, and a spring to pull the seal disc upward to seal the opening 61. This modified lid comprises air impermeable membrane 3, enforcement ring 8 having two substantially vertical ring connected to the outer perimeter 2 of the membrane at their top ends and a substantially horizontal ring connecting the lower ends of the two vertical rings 91, and a film strip 68 having one side attached to the membrane and a free end or handle 69 to allow one to pull the membrane. The horizontal ring 92 and vertical rings 91 of the enforcement ring 8 prevents any wrinkles from forming on the part of the membrane above the rim of the container as the membrane is pulled into the container. During use, the lid 1 is placed on the container that has product 26 therein and rests on a plate 67, the skirt or chamber 44 is placed over the container to form a seal between the seal ring 42 and plate 67, the air in both the chamber 44 and container 20 is removed by vacuum device 41, and the button 58 is pushed to allow air to enter the skirt chamber 44. The air pressure in the skirt chamber pushes the membrane 3 into the container 20 and causes the membrane to conform to the topographies of the side wall of the container and the product (FIG. 5 a). It is appreciated that by having a center bulge or cavity similar to the cavity 14 of FIGS. 3 and 4 on the impermeable membrane 3, the lid can seal a container 20 that has a very short side wall 21 or even no side wall (FIG. 5 b). The cavity or bulge on the membrane 3 accommodates the protruded product 26 in the container so that the perimeter area 2 of the membrane can reach and contact the rim or outer edge of the container before the skirt chamber 44 and container 20 are evacuated by the vacuum pump 46.

FIG. 6 shows a modified version of the lid 1 of FIG. 5 for use with a container 20 with a rim 21 that comprises a fusible material adapted to be fused to a fusible material on the impermeable membrane 3 by heat, adhesive, vibration or light beam welding and that is sufficiently strong to prevent the outer perimeter of the membrane from being substantially deformed as the membrane is pulled down into the container. The skirt 44 of the vacuum device has a collapsible lower skirt 44 a to allow the top wall of the skirt to fall down, thus causing the heating ring 128 to contact the membrane near the rim 21 of the container, when a vacuum is formed inside the skirt by device 41. A plurality of air shallow channels (not shown) are formed on either the membrane 3 or the rim to allow air to exit the container via the interface between the membrane and rim 21 after the collapsible lower skirt 44 a has been collapsed by the vacuum therein. During use, the lid 1 is placed on the rim 21, which is designed to function as the enforcement ring, of the container 20 that has product 26 therein and rests on plate 67; the skirt chamber 44 is placed over the container to form a seal between the seal ring 42 and plate 67; the air in chamber 44 is removed by vacuum device 41 and lower skirt 44 a collapsed to cause the heater ring 128 to press onto the membrane above the rim 21; the air in container 20 is drawn into the skirt chamber via the shallow air channels; the heater ring 128 is turned on briefly to fuse the fusible materials on the membrane and rim; and the button 58 is pushed to allow air to enter the skirt chamber 44 and cause the lower skirt to return to its original shape. The air pressure in the skirt chamber pushes and elongates the membrane 3 into the container 20 and causes the membrane to conform to the topographies of the side wall of the container and the product (FIG. 6 a). It is also appreciated that in Figs. Sand 6, the plate 67 may be replaced by a conveyor belt. In use, after the container 20 with product 26 and lid 1 is palced onto the belt, the conveyor belt transports the container to a location below the skirt chamber 44 and the skirt chamber lowers to the belt to evacuate and seal the chamber as described above.

FIGS. 7 a and 7 b show two exemplar structures for the air impermeable membrane 3. The membrane 3 of FIG. 7 a has a rubber or elastomer layer 72, a barrier polymer layer 70 and a tie or adhesive layer 71. The membrane 3 of FIG. 7 b has a rubber or elastomer layer 72, a barrier polymer layer 70, a skin or sealant layer 73, and two tie or adhesive layers 71 to bond the elastomer layer, barrier layer and sealant layer. The sealant layer 73 allows the enforcement ring 8 and the push facilitator 38 to be heat-sealed to the membrane. The elastomer layer 72 is at least about 150%, preferably about twice, as thick as the barrier layer 70, to allow the membrane to return substantially to its original shape after the vacuum below the membrane in the container is released.

The elastomer layer may be made from a thermoplastic elastomer and a natural or synthetic rubber such as butyl rubber, ethylene acrylic elastomer, EPDM or polyurethane elastomer. The polymeric barrier layer 70 is designed to retain its barrier to air after the membrane is expanded by force or vacuum, and may be made from low tensile strength barrier polymer such as polyethylene vinyl alcohol (EVOH), polyvinylchloride, or polyvilidene dicholoride. The sealant layer may be made from low tensile strength and low melting temperature polymers such as linear low or ultra linear low density polyethylene, polyethylene vinyl acetate (EVA) or thermoplastic elastomer. The membrane may be produced by co-extrusion, extrusion coating or lamination process. It is appreciated that when butyl rubber or ethylene acrylic elastomer that has high barrier to air is used, the membrane 3 can be a single layer membrane made of the butyl rubber or ethylene acrylic elastomer. It is also appreciated that by selecting the proper materials to enable the membrane 3 to have sufficiently low tensile strength or tensile stress at 20% to 100% elongation, the rate for the air to enter the space between the membrane 3 of the lid 1 and the container 20 would be significantly reduced. As a result, the single layer membranes made from the polymers such as polyethylene propylene elastomer (EPDM), polyurethane elastomer or low density polyethylene that have relatively low barrier to air but have sufficiently low tensile stress may be successfully used as the membrane 3 for the lid 1.

FIG. 8 shows a seventh modified version of the lid 1 of FIG. 1. In this modified lid 1, the membrane 3 is attached to the under surface of the horizontal ring 92 of the enforcement ring 8. A support plate 129 is positioned above the membrane and connected to the enforcement ring 8. A sufficient thick air space 19 is formed between the support plate and membrane to facilitate the formation of the airtight seal between the membrane and the container. An opening 79 is formed on the membrane to communicate the sufficient thick air space 19 with the container. During use, the lid is placed on the container and the membrane automatically conforms to the shape of the rim 21 to fill into the lower spaces 28 on the rim. A vacuum device such as the device 41 of FIG. 2 is then connected to the evacuation passageway 63 to evacuate the container and the resulting vacuum causes the membrane 3 to affix to the container 20. Here the opening 79 helps preventing the membrane 3 from crushing the product 26 in the container (FIG. 8 a). It is appreciated that the support plate 129 needs to be sufficiently thick to prevent the vacuum in the container from drawing the support plate down and that if the support plate is not strong enough to stay flat, the vacuum in the container 20 may be lost in a short period of time. It is also appreciated that such thick support plate 129 greatly increases the cost of the lid 1.

FIG. 9 shows an eighth modified version of the lid 1 of FIG. 1 for use with a lid support 142 to seal to a container. The lid 1 comprises the impermeable membrane 3 attached to the under surface of the horizontal ring 92 of the enforcement ring 8, a plurality of openings 77 formed on the membrane and a microporous membrane 9 attached to the membrane to prevent the particular matters in the product 26 from exiting the container via openings 77. The lid support 142 comprises a sufficiently thick horizontal support plate 129 to prevent deformation by the vacuum below it, a side wall 129 a, an air evacuation passageway 63 having a valve 94, a thick rubber gasket 30, and a sufficiently air space 19 below the gasket to prevent the rubber gasket from interfering the formation of intimate contact between the membrane 3 and the rim 21 after the lid 1 and lid support 142 are placed on the container. The valve 94 comprises a cylindrical valve body 15, an valve opening 5, a seal chamber 81 having a bottom wall 6 for closing the valve opening and an upper wall 82 with an opening, a knob 84 rotationally connected to the valve body 15 via threads (not shown), a presser 123 having a plunger 103 slidingly received in the seal chamber 81 and a stem 86 slidingly received in the opening on the upper wall 82 for connecting the plunger to the knob. The threads on the presser and valve body 15 are configured to allow one to move the knob 84 among a first position at which the seal chamber can freely move up and down to allow the removal of air from the container, a second position at which the plunger presses the bottom wall 6 against the valve opening 6 and a third position at which the plunger lifts the seal chamber up to allow air to enter the container 20. During use, one places the lid 1 on the container 20, causing the membrane 3 to conform to the topography of the rim 21. One then places the lid support on the lid 1, causing the side wall 129 a of the lid support to seal to the membrane 3 of the lid. The container is evacuated by connecting a vacuum device 41 (not shown) to the evacuation passageway 63. The vacuum in the container 20 draws the lid support 142 down to the container and causes the rim 21 to press against the membrane 3 and seal gasket 30 (FIG. 9 a). It is appreciated that in the lid 1 of FIG. 9 the enforcement ring 8 may be replaced by pressure sensitive adhesive or cling agent on the impermeable membrane, which adhesive or cling agent allows one to adhere the outer perimeter of the membrane 3 on to either side wall 129 a of the lid support 142 or the side wall 21 of the container.

FIG. 10 shows a ninth version of the lid 1 of FIG. 1 for providing hot gaseous fluid to a container 20 such as a bowl, plate or cup for heating or cooking the product 26 such as potatoes, eggs, meat, flour or grain products, or vegetables in the dish. A major problem encountered in commercializing the device that cooks food directly in a dish with hot gaseous fluid, which was taught in U.S. Pat. No. 6,582,743 by the inventor, is the inability to form a seal between an applicator lid and the rim of the dish 20. The lack of seal between the applicator lid and the rim of the dish results in significant loss of the hot gaseous fluid, which not only wastes energy but also makes the food less flavorful.

This modified lid comprises a sufficiently flexible membrane 3 with its perimeter 2 clamped in the enforcement ring 8, a support plate 129 positioned above the membrane and connected to the enforcement ring, a sufficient thick air space 19 between the support plate 129 and the membrane 3 to facilitate the formation of the airtight seal between the membrane and the rim 21 of the container, and a hot gaseous fluid passageway 63 a. The passageway 63 a has an outer cylinder 97 received by a central opening 88 of the support plate 129, a inner cylinder 98 having a fringe 96 attached to the top end of the outer cylinder and hot gas outlet 5 for the hot gaseous fluid to exit the container, and a ring shaped channel 95 between the inner and outer cylinders to function as the distributor inlet for distributing the hot gaseous fluid from a generator 117. The outer cylinder has having a ring-shaped locker 87 supported by the part of the support plate around the opening 88 and an elastic ring member 89 that presses the membrane 3 against the undersurface of the support plate 129 after the ring-shaped locker 87 is pushed through the opening 88 and becomes supported by the part of the support plate around the opening 88.

The hot gaseous fluid generator 117 comprises a fluid connector 74 having an upper chamber 76 to receive the inner cylinder 98 of the lid 1 and a lower cylinder 75 for receiving the outer cylinder 97, a heater 116 in a heating chamber 115 for heating a gaseous fluid and/or evaporating water, and a temperature controller 119 for one to control the temperature of the hot gaseous fluid. The generator also comprises a turbine blade 114 housed in a pump chamber 112 and connected to motor 109 via an rod 111 for drawing the hot gaseous fluid from the container 20 via outlet 5 of the lid and conduit 100 back into the pump chamber, pushing the gaseous fluid through the opening 121 to heater 116 to heat the gaseous fluid to a desired temperature, and delivering the heated gaseous fluid back to the container 20 via a conduit 122, a ring-shaped channel 78 of the fluid connector 74 and the ring-shaped channel 95 of the lid 1. For simplicity, the motor 109 and blade 114 are called gas pump. The generator also has water reservoir 102 for water 103, a water pump 101 connected to the reservoir via tube 104 and to an inlet 109 at the top of the pump chamber via a water passageway 107. The water is delivered by the pump 101 via inlet 109 to blade 114 where the water atomized or misted before it is blown to the heater 116 to be evaporated to generate steam. A valve 106 is located in the water passageway 107 to control the water flow rate or the amount of water delivered to the blade 112 and heater 116 by the pump 101. A humidity meter 125 may be placed in the conduit 100 for measuring the humidity of the hot gaseous fluid and providing an electric signal to the liquid pump 101 or the valve 106 to stop the delivery of water to the heater 116 when the humidity is above a predetermined value and to start delivery of water to the heater when the humidity is below a predetermined value. A air valve 110 is located on the top end of the pump chamber, i.e. at the low pressure side of the blade, for controlling the amount of air available to the blade or gas pump, thereby controlling the percent of hot air in the hot gaseous fluid.

To use the lid 1 and the hot gaseous fluid generator 117, one places the lid on the dish plate 20 containing the food 26 to be heated or cooked and the membrane 3 conforms to the topography of the rim 21 to form an airtight seal to the rim. The fluid connector 74 is placed over the fluid passageway 63, causing the inner and outer cylinders 98 and 97 of the fluid passageway 63 to enter the upper and lower chambers 78 and 75 of the fluid connector 74, respectively. One then selects the temperature and humidity level for the hot gaseous fluid and turns on the gas pump or motor 109 to deliver the hot gaseous fluid from the gas pump or pump chamber 112 to the product 26 in dish plate 20 via heater 116, conduit 122 and inlet channel 95, and to draw the hot gaseous fluid from the container 20 back to the pump chamber 112 via outlet 5, chamber 76 and conduit 100. As a result, the hot gaseous fluid is circulated between the container and the gas pump chamber. To increase the humidity in the hot gaseous, more water is pumped by pump 101 to the blade 114; to decrease humidity, more air is let into the pump chamber via the air valve 110. At the end of cooking or heating, the air valve 110 may be fully opened and the heater 116 is turned off to pump ambient temperature air to the dish plate to cool the dish plate to a certain degree to make it safe to touch. It is appreciated that the lid 10 will be lifted up by the pressure in the dish plate 20 to form a gap between the membrane 3 and the rim 21 of the dish plate to release some gaseous fluid when the pressure below the membrane reaches a predetermined value, as taught in U.S. Pat. No. 6,582,743 by the inventor. It is also appreciated that the water pump 101 may be replaced by a porous hydrophilic wick sheet having one end dipped into the reservoir and the other end located in the circulation passageway for the hot gaseous fluid. It is also appreciated that either ˜100% steam may be used as the hot gaseous fluid or nearly 100% hot air may be used as the hot gaseous fluid to treat the product 26 below the membrane 3 in dish plate 20.

The scope of the invention is obviously not restricted or limited to the embodiments described by way of examples and depicted in the drawings, there being numerous changes, modifications, additions, and applications thereof imaginable within the purview of the claims. 

1. A lid for sealing a container having an opening for allowing a product to be placed into the container, a side wall and a rim at the free end of the side wall under a subatmospheric pressure or vacuum to increase the life of the product, said lid comprising a substantially impermeable membrane having an outer perimeter at least as large as the rim of the container to cover the container and an enforcement means for preventing said outer perimeter from substantial deformation when said membrane is being elongated, said membrane being adapted to enter the container to contact at least part of the side wall of the container as well as to wrap around at least the top end of the product therein when a subatmospheric pressure or vacuum is formed in the space between said membrane and the container, thereby causing said membrane to conform substantially to the topographies of the side wall of the container and the product to prevent the container from being imploded or collapsed by said vacuum or subatmospheric pressure.
 2. A lid as defined in claim 1 wherein said impermeable membrane is adapted to be sufficiently expandable or stretchable to prevent breakage or puncture by the product, and adapted to have a tensile stress lower than 2R_(p)/L pounds per square inch at a tensile strain of approximately 20% to 50% elongation to prevent said membrane from crushing or damaging the product under said subatmospheric pressure, wherein R_(p) and L are the radius or equivalent radius of the product and the membrane thickness in inches, respectively.
 3. A lid as defined in claim 1 wherein said impermeable membrane is adapted to be sufficiently expandable or stretchable to prevent breakage or puncture by the product, and adapted to have a tensile stress lower than 2R_(m)/L pounds per square inch at a tensile strain of approximately 20% to 50% elongation to prevent said membrane from substantially deforming the container that has a thin or weak wall under said vacuum or subatmospheric pressure, wherein R_(m) and L are the radius or equivalent radius and thickness of said membrane in inches, respectively, thereby saving the amount of materials used to construct the container.
 4. A lid as defined in claim 1 wherein said impermeable membrane is adapted to retain at least a substantial part of its barrier to air after being expanded or stretched into the container, and adapted to have a tensile stress sufficiently low to reduce the rate of air diffusion through said membrane into the container under said subatmospheric pressure.
 5. A lid as defined in claim 4 wherein said tensile stress is adapted to be lower than 5R_(m)/L pounds per square inch at a tensile strain of approximately 20% to 50% elongation, wherein R_(m) and L are the radius or equivalent radius and thickness of said membrane in inches, respectively.
 6. A lid as defined in claim 1 wherein said enforcement means comprises an enforcement ring permanently connected to said outer perimeter or to a region near said outer perimeter on said impermeable membrane, said enforcement ring being adapted to prevent any wrinkles from forming on the section of said membrane located above the rim or side wall of the container as said membrane is pulled down to conform substantially to the topographies of the side wall of the container and the product by the subatmospheric pressure or vacuum.
 7. A method for using the lid of claim 6 comprising placing a product into the container, placing said lid on the container in such a way that said enforcement ring is outside the rim of the container, removing air in the space between said membrane and the container to create a vacuum or subatmospheric pressure therein, and allowing the air or gas pressure above said membrane to cause said membrane to elongate and conform to the topographies of the side wall of the container and the product.
 8. A lid as defined in claim 1 wherein said enforcement means comprises a first fusible material on said impermeable membrane and a second fusible material on the rim of the container adapted to fuse to said first fusible material on the perimeter area of said impermeable membrane, thereby enabling the rim of the container to prevent said outer perimeter of said impermeable membrane from being substantially deformed as said membrane is pulled down to conform substantially to the topographies of the side wall of the container and the product by the subatmospheric pressure or vacuum.
 9. A method for using the lid of claim 8 comprising placing a product into the container, placing said lid on the rim of the container, enclosing the container with said membrane thereon in a vacuum chamber to remove air in the space between said membrane and the container to create a vacuum or subatmospheric pressure therein, fusing said first material on the perimeter area of said membrane to the second material on the rim of the container in the vacuum chamber, and allowing air or gas to enter the vacuum chamber, the air or gas pressure causing said membrane to elongate and conform to the topographies of the side wall of the container and the product.
 10. A lid for forming an airtight seal to a container having an open end for receiving a product into the container, a side wall and a rim at the free end of the side wall, said lid comprising an air impermeable membrane having an outer perimeter at least as large as the rim of the container and an enforcement ring permanently connected to said outer perimeter or to an area near said outer perimeter on said membrane for facilitating the formation of an airtight seal between said membrane and the rim of the container, said membrane being sufficiently flexible and adapted to enable the part of said membrane that is in contact with the rim or side wall of the container to conform to the topography of the rim or side wall to prevent any air passageway from being formed between said membrane and the rim or side wall of the container.
 11. A lid as defined in claim 10 wherein said membrane is adapted to be stretched at least partially into the container by hand or force to drive air out of the container, said membrane being further adapted to have a tendency to return to its original shape to generate a subatmospheric pressure or vacuum in the container, thereby affixing said membrane to the rim of the container at least in part by said subatmospheric pressure.
 12. A lid as defined in claim 10 wherein said air-impermeable membrane is adapted to sink into the container to contact the side wall of the container when a subatmospheric pressure or vacuum is formed in the space between said membrane and the container, thereby reducing the risk of implosion or collapse of the container by said subatmospheric pressure or vacuum.
 13. A lid as defined in claim 12 wherein said impermeable membrane is sufficiently thin to enable said membrane to wrap around at least the top end of the product in the container when the subatmospheric pressure or vacuum is formed in the space between said membrane and the container.
 14. A lid as defined in claim 10 wherein said air impermeable membrane is an elastic or rubbery membrane adapted to be stretched by a subatmospheric pressure in the container and to return substantially to its original shape after removal of said subatmospheric pressure.
 15. A lid as defined in claim 10 wherein said membrane comprises a bulge adapted to accommodate at least a part of the product in the container to enable an intimate contact between the peripheral area of said membrane and the rim of the container in case that the product protrudes out of the container or that the container has too short a side wall or no side wall.
 16. A lid as defined in claim 10 wherein said enforcement ring is adapted to have sufficient resistance to both horizontal and vertical deformation when said membrane is being pushed down by hand or force or pulled down by a partial vacuum into the container, thereby preventing the formation of wrinkles on said membrane and air channels between said membrane and the rim or side wall of the container.
 17. A lid as defined in claim 16 wherein said enforcement ring comprises a first ring and a second ring permanently connected to said first ring at an angle smaller than 180 degrees.
 18. A lid as defined in claim 16 wherein said enforcement ring further has a third ring connected to said second ring to clamp the peripheral section of said membrane between said first and third rings.
 19. A lid as defined in claim 16 wherein said enforcement ring adopts one of a substantially circular shape, a substantially oval shape, and a substantially rectangle or square shape with rounded corners to help preventing said horizontal deformation when said membrane is being pushed or pulled into the container.
 20. A lid as defined in claim 10 wherein said membrane is made from a rubber or elastomer material selected from the group consisting of butyl rubber and ethylene acrylic elastomer, thereby providing said membrane sufficient barrier to air when said membrane is at its elongated or stretched state.
 21. A lid as defined in claim 10 wherein said air-impermeable membrane comprises a polymeric barrier layer adapted to retain at least some of its barrier to air after said membrane is pushed by force or pulled by a subatmospheric pressure or vacuum into the container.
 22. A lid as defined in claim 21 wherein said membrane comprises an elastomer layer selected from the group consisting of natural rubber, synthetic rubber and thermoplastic eleatomer.
 23. A lid as defined in claim 22 wherein said elastomer layer is at least twice as thick as said polymeric barrier layer, thereby allowing said membrane to return substantially to its original shape when the pressure below said membrane reaches atmospheric pressure.
 24. A lid as defined in claim 10 wherein said air impermeable membrane comprises a material adapted to fuse to said enforcement ring when heated by heat, vibration or light energy.
 25. A lid as defined in claim 10 further comprising a handle having a first end attached to said membrane and a second end adapted for a user to pull to create an air passageway between said membrane and the container to allow air to enter the container, thereby facilitating the removal of said lid from the container.
 26. A lid as defined in claim 10 further comprising a film strip attached to said membrane in such a way that an air passageway is created between said membrane and the container by pulling up on an unsecured end portion of said film strip, thereby allowing air to enter the container to facilitate the removal of said lid.
 27. A lid as defined in claim 10 wherein said membrane further comprises an opening to allow hot gaseous fluid from a generator to be introduced to the product in the closed space between said membrane and the container, thereby causing the product to be heated or cooked.
 28. A lid as defined in claim 10 further comprising an inlet connected or adapted to connect to a generator to introduce hot gaseous fluid from the generator to the product in the closed space between said membrane and the container, thereby causing the product to be heated or cooked.
 29. A lid as defined in claim 10 further comprising a plate above said membrane and connected to said enforcement ring and an air space between said plate and said membrane.
 30. A lid as defined in claim 10 further comprising an inlet for receiving hot gaseous fluid from a generator, said lid being adapted to form a gap between said membrane and container to release some hot gaseous fluid when the pressure below said membrane reaches a predetermined value.
 31. A lid as defined in claim 10 further comprising an inlet for introducing hot gaseous fluid from a generator into the container and an outlet for returning at least part of the hot gaseous fluid to the generator, thereby causing circulation of the hot gaseous fluid between the generator and the closed space defined by said membrane and the container to heat or cook the product.
 32. A lid as defined in claim 31 further comprising said generator having a heater for evaporating the water from a reservoir to produce hot steam and an gas pump for circulating hot gaseous fluid comprising hot steam in a loop comprising said heater, said inlet, said closed space, said outlet and said gas pump.
 33. A lid as defined in claim 32 wherein said generator further comprises a liquid pump for delivering water to said heater and a metering device for controlling the amount of water delivered to said heater.
 34. A lid as defined in claim 33 wherein said metering device comprises a humidity meter for measuring the humidity of the hot gaseous fluid and providing an electric signal to said liquid pump or a valve to stop the delivery of water to said heater when the humidity is above a predetermined value and to start delivery of water to said heater when the humidity is below a predetermined value.
 35. A lid as defined in claim 32 wherein said gas pump comprises a blade for converting the water from the reservoir into microscopic droplets or mist and delivering the droplets or mist to said heater.
 36. A lid as defined in claim 32 wherein said generator further comprises an air valve for controlling the amount of air available to said gas pump, thereby controlling the percent of hot air in the hot gaseous fluid.
 37. A lid as defined in claim 31 further comprising said generator having a heater for heating air to produce hot air and an gas pump for circulating the hot gaseous fluid comprising hot air in a loop comprising said heater, said inlet, said closed space, said outlet and said gas pump.
 38. A lid as defined in claim 31 further comprising said generator having a heater for producing hot gaseous fluid and a gas pump for circulating hot gaseous fluid in a loop comprising said heater, said inlet, said closed space, said outlet and said gas pump, said generator being adapted to deliver ambient air to the container via said inlet to cool said membrane and the container after finishing heating or cooking the product.
 39. A lid as defined in claim 10 further comprising a thin layer of fluid on said membrane to prevent or retard air from entering the container, said fluid being one of a liquid, paste and gel.
 40. A lid as defined in claim 10 wherein said air impermeable membrane further comprises a tacky or adhesive material to cause said membrane to reversibly adhere to the container to prevent or retard air from entering the container.
 41. A lid as defined in claim 10 wherein said air impermeable membrane is substantially transparent to light to make the product in the container visible, and said membrane further comprises an effective amount of an antifogging additive to ensure clear visibility of the product through said membrane.
 42. A lid as defined in claim 10 wherein said impermeable membrane is adapted to be sufficiently expandable and to have a tensile stress sufficiently low to retard air from entering the container under a subatmospheric pressure or vacuum.
 43. A lid as defined in claim 10 wherein said air impermeable membrane is adapted to enable one to push said membrane into the container to drive air out of the container, said membrane being further adapted to generate a partial vacuum in the container by simply stopping pushing said membrane.
 44. A lid as defined in claim 43 further comprising a push facilitator on or attached to said membrane for facilitating one to push said membrane into the container, said facilitator being substantially more rigid than said membrane.
 45. A lid as defined in claim 10 wherein said impermeable membrane is adapted to be sufficiently expandable and to have a tensile stress lower than 3R_(m)/L pounds per square inch at a tensile strain of approximately 20% to 50% elongation to enable said lid to be used seal a container having a relatively thin or weak wall under a subatmospheric pressure, wherein R_(m) and L are the radius or equivalent radius and thickness of said membrane in inches, respectively.
 46. A lid as defined in claim 10 wherein said air impermeable membrane comprises a side wall section, at least part of which has a perimeter smaller than the rim of the container, and a substantially horizontal center section, at least said side wall section of said membrane being rubbery or elastic in order to form an airtight seal between the rim of the container and said side wall section.
 47. A lid as defined in claim 46 wherein said substantially horizontal center section of said impermeable membrane is adapted to be pushed at least partially into the container by hand or force, said membrane being adapted to have a tendency to return to its original shape to cause a vacuum or subatmospheric pressure in the container to improve the sealing of said lid to the rim of the container.
 48. A lid as defined in claim 46 wherein said enforcement ring is larger than at least part of said side wall section of said membrane to facilitating the mounting and sealing of said lid to the container.
 49. A lid as defined in claim 46 wherein said enforcement ring is elastic.
 50. A lid as defined in claim 46 wherein said side wall section is adapted to have a sufficiently low strength to reduce the force needed to stretch said side wall section to enlarge the diameter of said side wall section, thereby facilitating the mounting of said lid over the container.
 51. A lid as defined in claim 46 further comprising a valve having a vent opening on said horizontal center section of said membrane and a seal member connected to said membrane for covering said vent opening, said seal member being adapted to open when one places said lid over the container and pulls said enforcement ring downward to allow the air enclosed between said membrane and the container to escape through said vent opening, thereby reducing the force needed to pull said enforcement ring downward to cause said side wall section of said membrane to form a sufficient seal to the rim of the container.
 52. A lid for forming an airtight seal to a container such as a bowl, dish plate, canister, cup, jar, tray or bottle that has an open end, a bottom, a side wall between the open end and bottom, and a rim at the open end, said lid comprising an air-impermeable membrane having an outer perimeter at least as large as the rim of the container to cover the open end of the container and an air evacuation passageway comprising a valve for allowing air to be evacuated from the container but preventing air from entering the container via said evacuation passageway, said membrane being sufficiently flexible to enable the part of said membrane above the rim or side wall of the container to conform to the topography of the rim or side wall to prevent air passageway from forming between said membrane and the rim or side wall of the container.
 53. A lid as defined in claim 52 wherein said evacuation passageway further comprises a film having numerous microscopic openings adapted to allow air to exit the container but to prevent particulate or solid matters from passing through, thereby preventing the loss of product when the container is evacuated via said evacuation passageway.
 54. A lid as defined in claim 53 wherein said film is sufficiently hydrophobic to become impermeable when liquid reaches said film, thereby preventing the loss of liquid in the product when the container is evacuated via said evacuation passageway.
 55. A lid as defined in claim 52 wherein said impermeable membrane is adapted to be pushed at least partially into the container by hand or force to evacuate air out of the container via said evacuation passageway, said membrane being further adapted to have a tendency to return to its original shape to generate a subatmospheric pressure in the container, thereby causing said lid to seal to the container at least in part by said subatmospheric pressure.
 56. A lid as defined in claim 55 further comprising a push facilitator attached to said membrane apart from said enforcement ring to avoid weakening the seal between said membrane and container.
 57. A lid as defined in claim 52 further comprising an enforcement ring connected to said outer perimeter or to a region near said outer perimeter on said impermeable membrane for preventing substantial deformation of said outer perimeter of said membrane when said membrane is elongated by force or vacuum, thereby facilitating the formation of the airtight seal between said membrane and the container.
 58. A lid as defined in claim 57 further comprising a support member positioned above said membrane and connected to said enforcement ring and an air space between said support member and said membrane to facilitate the formation of the airtight seal between said membrane and the container.
 59. A lid as defined in claim 58 further comprising a rubber gasket in said air space, said rubber gasket is sufficiently thinner than an air space so that said impermeable membrane is apart from said rubber gasket to facilitate the formation of said airtight seal.
 60. A lid as defined in claim 52 wherein said membrane is selected from the group consisting of a rubber or elastomer membrane and a composite membrane having an elastomer layer and at least one of a readily stretchable polymeric barrier layer and sealant skin layer.
 61. A lid as defined in claim 52 wherein said valve comprises a seal member, a valve opening normally closed by said seal member, and an elongated member having one end connected to said seal member and a free end, said seal member being adapted to open said valve opening when air is evacuated from the container or when one pulls said free end of said elongated member, said elongated member being adapted to be sufficiently flexible to prevent unintended release of the vacuum in the container when said elongated member is accidentally touched by another container or object.
 62. A lid as defined in claim 52 wherein said valve comprises a valve opening through said membrane, a seal member located below said membrane, a retainer located above said membrane and connected to said seal member by a stem, and a spring for pulling said seal member upwards to close the valve opening, said retainer, seal member and spring being configured to allow one to apply a sufficient force to said retainer to push said seal member down to open said valve opening and push said membrane into the container to drive air out of said valve opening and to remove said sufficient force to cause a subatmospheric pressure or vacuum in the container, and to allow one to apply to said retainer a smaller force large enough to push said seal member down to release said vacuum but small enough to allow said membrane to return to its original shape.
 63. A lid as defined in claim 52 wherein said valve comprises a valve body, an valve opening, a seal chamber having a bottom wall adapted to close said valve opening and an upper wall with an opening, a knob rotationally connected to said valve body, a presser having a plunger slidingly received in said seal chamber and a stem slidingly received in said opening on said upper wall for connecting said plunger to said knob, said knob being adapted to move among a first position at which the seal chamber can freely move up and down to allow the removal of air from the container, a second position at which the plunger presses said bottom wall of said seal chamber against said valve opening and a third position at which the plunger lifts said seal chamber up to allow air to enter the container.
 64. A lid for sealing a container having an opening for allowing a product to be placed into the container, a side wall and a rim at the free end of the side wall under a subatmospheric pressure or vacuum to increase the life of the product, said lid comprising a thin body affixed on the side wall of the container to close the opening of the lid at least in part by the subatmospheric pressure or vacuum in the container and a valve having a seal member located above said thin body, a valve opening on said thin body and normally closed by said seal member, and a slender member having one end connected to said seal member and a free end, said seal member being adapted to open said valve opening when one pulls said free end of said slender member, said slender member being adapted to be sufficiently flexible to prevent unintended release of the vacuum in the container when said slender member is accidentally touched by another container or object.
 65. A lid as defined in claim 64 further comprising a chamber for preventing said seal member from being accidentally touched by another container or object to cause unintended release of the vacuum in the container, said chamber having an opening for allowing said free end of said slender member to pass through.
 66. A lid as defined in claim 64 further comprising a thin fluid layer including one of a high boiling point liquid layer, a gel and a paste layer on said seal member to facilitate the closure of said valve opening.
 67. A lid as defined in claim 64 further comprising a retainer below said thin body and connected to said seal member by a stem in such a way that said thin body is between said seal member and said retainer, said retainer being adapted to apply an elastic tension to said seal member to cause said seal member to seal said valve opening even after the loss of vacuum in the container, said elastic tension being sufficiently small to allow the opening of said valve by pulling said free end of said slender member.
 68. A lid as defined in claim 64 wherein said lid further comprises a film having numerous microscopic openings adapted to prevent particulate or solid matters from passing through said valve opening.
 69. A lid as defined in claim 68 wherein said film is sufficiently hydrophobic to retain its permeability to air after the liquid in the product contacted said film, thereby enabling air to enter the container when said free end of said slender member is pulled.
 70. In a container having a top part and a bottom part sealed or adapted to seal to said top part to enclose a product under a subatmospheric pressure or vacuum to increase the life of the product, the improvement comprising a substantially air impermeable membrane for at least one of said top and bottom parts of the container, said air impermeable membrane comprising a material having sufficient barrier to air to maintain said subatmospheric pressure for an extended period of time and being capable of expanding or stretching at least 50% prior to causing any significantly deterioration of said sufficient barrier to air by said subatmospheric pressure or vacuum, thereby allowing said membrane to wrap around at least the part of the product, said membrane being configured to have a tensile stress lower than 2R_(p)/L pounds per square inch at a tensile strain of approximately 20% to 50% elongation to prevent said membrane from crushing or damaging the product under said subatmospheric pressure, wherein R_(p) and L are the radius or equivalent radius of the product and the membrane thickness in inches, respectively.
 71. A lid as defined in claim 70 wherein said tensile stress is adapted to be lower than 0.5R_(p)/L pounds per square inch at a tensile strain of approximately 20% to 50% elongation to enable the product to be a crushable or delicate selected from the group consisting of fruit, vegetables, fried product, baked product, dried species and fragile items below said membrane when said vacuum or subatmospheric pressure is present.
 72. A lid as defined in claim 70 wherein said membrane is a rubber or elastomer membrane.
 73. A lid as defined in claim 70 wherein said membrane is a composite membrane having a rubber or elastomer layer and at least one of a readily stretchable polymer barrier layer and sealant layer. 